DocInfo.rev_seq is declared as 64-bit, but only 32 bits are persisted

couch_common.h declares the field DocInfo.rev_seq as type uint64_t. However, the database only persists it as a 32-bit value (see assemble_seq_index_value, couch_save.c:19). This means that clients trying to set values larger than 2^32-1 will find the upper 32 bits truncated when they read the document.

The field should be changed to type uint32_t. This could cause warnings in client code if it's assigning a 64-bit value to it, but I don't believe any of our code uses this field at all, currently(?)